The present invention relates to a heating apparatus for heating an advancing yarn and which is particularly adapted for use in a yarn false twist crimping machine.
Heating apparatus of the described type are known from both German OS 23 14 975 and British Patent 890,057. In these known heating apparatus, the yarn is guided along a heated surface, which has a temperature substantially higher than the target temperature of the yarn, the target temperature of the yarn being the temperature to which the yarn is to be heated. Such heating apparatus are used primarily in yarn false twist crimping machines for crimping synthetic filaments yarns, with the target temperature ranging from 150.degree. to 230.degree. C. The temperature of the surface is substantially higher than 300.degree. C.
In the known heating apparatus, the yarn is guided by spaced-apart yarn guides at a distance from the heated surface. The arrangement of the yarn guides along a convexly curved line permits a full contact of the yarn with the yarn guides and a smooth threadline.
However, it has been found that the looping angle of the yarn on each individual yarn guide as well as the sum of the looping angles are very significant for the smoothness of the yarn path and the amount of the false twist to be imparted to the yarn. In the known heating apparatus, however, the predetermined looping angle and the total looping angle also influence the distance of the yarn from the heating surface.
It is accordingly an object of the present invention to guide a yarn along the heating apparatus, in such a manner that it becomes possible to freely select the looping angle on the yarn guides and the sum of the looping angles on all yarn guides, without it being necessary to also influence the distance of the yarn path from the heating surface.